Among insect pest control products for controlling flying insect pests such as mosquitoes and the like are so-called “liquid mosquito killers,” which are commercially available. Liquid mosquito killers utilize the technique of putting an absorbent wick in a chemical liquid containing an insecticidal component, allowing the chemical liquid to be absorbed and transported to the top portion of the absorbent wick, and heating the absorbent wick so that the insecticidal component is vaporized and diffused into the atmosphere. Chemical liquids for use in liquid mosquito killers are roughly divided into kerosene-based formulations (referred to as “oil-based formulations”) and water-based formulations. Most of the conventional liquid mosquito killers include an oil-based formulation. However, water-based formulations may have advantages over oil-based formulations in terms of usefulness and effectiveness. For example, Patent Document 1 and Patent Document 2 indicate that water-based formulations of insecticide may have a lower risk of catching fire and be more effective in killing insect pests, compared to oil-based formulations of insecticide.
Typical insecticidal components for liquid mosquito killers are pyrethroid compounds. Of pyrethroid compounds, insecticidal components such as allethrin, prallethrin, furamethrin, and the like have been most commonly used, but lately there has been a trend towards using newer insecticidal components such as transfluthrin, metofluthrin, and the like, which have a higher insecticidal activity.
Transfluthrin, metofluthrin, and the like have high vapor pressure and different physical properties, compared to allethrin, prallethrin, and the like. Nevertheless, if an oil-based formulation of transfluthrin, metofluthrin, or the like is used in a liquid mosquito killer, then when an absorbent wick adapted to conventional pyrethroid compounds is directly used, a very significant problem does not arise. Meanwhile, if a water-based formulation of transfluthrin, metofluthrin, or the like is prepared, then when an absorbent wick for conventional pyrethroid compounds is used, the affinity of the water-based formulation for the absorbent wick may be unbalanced, so that the amount of the insecticidal component that is vaporized and diffused may become unstable, and therefore, the insect killing efficacy may be impaired, for example.
In order to solve these problems, the following measures may be taken: (1) improving a chemical liquid formulation; (2) modifying specifications of an absorbent wick; (3) changing or adjusting the temperature of a heat generator; and the like. Measure (3) (changing or adjusting the temperature of a heat generator) is not very practical, because conventional devices used as “liquid mosquito killers” have already been widespread on the market.
As to measure (1) (improving a chemical liquid formulation), Patent Document 3 discloses a mixture of a pyrethroid insecticidal component and a solvent having a high boiling point. Patent Document 3 discloses the formulation of an insect pest control liquid to be thermally vaporized and diffused, that contains metofluthrin and Thio tech (a mixture of paraffin and a naphthene hydrocarbon at a ratio of approximately 6:4). However, Thio tech is not soluble in water, and therefore, such a liquid formulation is, of course, not applicable to water-based liquid mosquito killers.
As to measure (2) (modifying specifications of an absorbent wick), Patent Document 4 discloses a baked molded article that contains aggregate including phosphorus oxide. Patent Document 4 discloses an absorbent wick having a specific surface area of 1.0-3.0 m2/g, a liquid absorption ratio of 15-35%, and a liquid absorption speed of 10-25 mm/h, and indicates that the absorbent wick having these properties is applicable to water-based formulations of chemical liquids.